Background: Accurate measurement of corneal thickness (CT) is highly important in decision making and planning for refractive surgery. It is also important in diagnosis of keratoconus, measuring intraocular pressure and monitoring corneal edema. Different methods are available for CT measurement including optical and ultrasound based techniques. Aim of the Study: was to assess the diagnostic accuracy of optical (AS OCT and Pentacam) and ultrasound imaging systems (USP) in measuring corneal thickness in healthy and diseased corneas. Materials and Methodology: Three groups were included: 20 healthy corneas, 20 eyes with keratoconus (KC) and 20 eyes with corneal scars. In all cases central corneal thickness (CCT) was measured using ultrasound pachymetry, Pentacam and anterior segment optical coherence tomography (AS OCT). Results: In normal corneas the mean difference (MD) between US and Pentacam, US and OCT & Pentacam and OCT (-1.3±9.4, 0.4±10.4 &1.7±10.7µm) to be statistically insignificant between the 3 pairs with coefficient of determination 1 between the 3 pairs. In KC group the mean difference (MD) between US and Pentacam (-7.7±15.1 µm) was statistically significant while the MD between US and OCT & Pentacam and OCT (4.7±15.7 and 12.3±14.1 µm) was not statistically significant. In scar group the MD between the 3 pairs (-1.1±79.1, -13.6±20.8 &-12.5±73.0) with statistically significant difference between USP and OCT. Coefficient of determination was found 0.9. Conclusion: USP, AS OCT and Pentacam have high agreement regarding CCT measurement in normal corneas. However, when we studied KC and scarred corneas we found that OCT measurements are higher than those of Pentacam in most of the cases regarding CCT.